The present invention is directed to powder metallurgical methods for producing materials including iron. More particularly, the present invention is directed to methods for producing materials including iron wherein all or a portion of a powder mix is molded and subsequently sintered.
The powder metal industry can trace its beginnings back to the development of the porous bronze bearing. In the early 1900""s, the emergence of small electrical motors created a market for a low-cost, efficient bearing material. It was found that if one blended copper and tin powders in about a 90:10 ratio, molded the mixture, and sintered the resulting compact in a protective atmosphere at 1500-1550xc2x0 F. (816-843xc2x0 C.), the product was a porous bronze alloy. This porous sintered compact could then be impregnated with oil to give an excellent bearing material, which was essentially self-lubricating and served for the life of the motor without further oiling.
Porous bronze and variations of it dominated the porous bearing market until the introduction of porous iron-graphite powder metal materials in the 1970""s. A motivation for development of an iron-graphite material was that the costs of iron and graphite powders were significantly lower than copper and tin powders.
An advantage of iron-graphite material produced by powder metallurgy techniques is that graphite particles in the material reduce friction between the material and supported moving parts. A problem encountered in producing iron-graphite bearings by powder metallurgy techniques, however, is the tendency for carbon to go into solution in iron at high temperatures. When this happens, hard phases (including pearlite and carbides) form in the iron-graphite material, which are abrasive and result in poorer bearing performance.
Early efforts to control the solution of graphitic carbon centered on the choice of graphite, the use of large particle size graphite, and the use of sulfur-containing iron powders. In addition, it was considered important to very closely monitor temperature while producing iron-graphite material to keep it below about 1900xc2x0 F. (1037xc2x0 C.) to inhibit solution of carbon. Even with tight temperature control, however, carbon solution may be a problem. Moreover, temperature control can reduce the strength of the bearing. If a typical conventional iron-graphite powder metal compact is sintered at less than about 1700xc2x0 F. (927xc2x0 C.), carbon absorption is inhibited, but part strength will be lower; on the other hand, if the part is sintered above about 1800xc2x0 F. (982xc2x0 C.), strength improves but problematic carbon solution increases.
Another approach to reducing the formation of carbides and other hard phases in sintered iron-containing powder metal bearing materials is to reduce or entirely eliminate graphite from the materials. Doing so with conventional iron-graphite powder mixes, however, may reduce the lubricity of the materials and their suitability for bearing applications.
Accordingly, a need exists for an improved method for producing iron-containing material by powder metallurgy techniques that may be used to produce bearing materials, as well as materials for other applications.
In order to address the above need, one aspect of the present invention is directed to a method of forming a powder metal material wherein the method includes molding a compact from a powder mix including at least one iron-containing powder and at least one glass, and subsequently sintering the compact. (As used herein, xe2x80x9cincludingxe2x80x9d means that other unspecified materials may be present. Also as used herein, xe2x80x9csubsequentlyxe2x80x9d means occurring later in time than, but not necessarily immediately after, a prior event or act.) In certain embodiments, the powder mix also includes at least one solid lubricant such as, for example, graphite or molybdenum disulfide. Materials made by the method of the present invention also are included within the present invention.
According to another aspect of the present invention, there is provided a powder metal material including iron and glass. Certain embodiments of the material also include at least one solid lubricant such as, for example, graphite or molybdenum disulfide.
According to yet another aspect of the present invention, there are provided articles of manufacture including materials within the present invention and/or which are made by a method within the present invention.
Yet another aspect of the invention is directed to methods for producing articles of manufacture, and which methods include the molding a compact from a powder mix including at least one iron-containing powder and at least one glass, and subsequently sintering the compact. In certain embodiments, the powder mix also includes at least one solid lubricant such as, for example, graphite or molybdenum disulfide.
The reader will appreciate the foregoing details of the present invention, as well as others, upon considering the following description of certain embodiments of the invention. The reader also may comprehend additional advantages of the present invention upon carrying out or using the invention. It will be understood that the following description necessarily is limited to only certain embodiments of the invention and is not exhaustive of the full range of embodiments of the invention.